This invention relates to an improved acoustic fluid emission head, e.g. an acoustic ink printhead, and a method of forming or assembling same. More particularly, the invention is directed to an acoustic ink printhead that advantageously incorporates elastomer gaskets to replace epoxy joints in the printhead and a corrugated spacer to provide focal gap control in the printhead. A related method for forming the printhead includes folding and spot-welding the aperture plate of the printhead to maintain the elastomer gaskets in place and, consequently, control the focal gap.
While the invention is particularly directed to the art of acoustic ink printing, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in any application where acoustic emitters are used.
By way of background, acoustic ink printing involves the emission of a droplet of ink from a pool of ink toward a print medium. Sound waves are generated and focussed toward the surface of the ink pool to emit the droplet therefrom. While acoustic ink printing elements may take various forms, such elements typically include a piezoelectric transducer, a lens, a cover plate having apertures formed therein to allow emission of the ink, and corresponding wiring. It is to be appreciated that approximately one thousand (1,000) or more of these elements may be disposed on a single printhead. It should also be appreciated that other fluids may be emitted such as molten metal, etc. rather than ink.
More particularly, as shown in FIG. 1, a single acoustic element 10 includes a glass layer 12 having an electrode layer 14 disposed thereon. A piezoelectric layer 16, preferably formed of zinc oxide, is positioned on the electrode layer 14 and an electrode 18 is disposed on the piezoelectric layer 16. Electrode layer 14 and electrode 18 are connected through a surface wiring pattern representatively shown at 20 and cables 22 to a radio frequency (RF) power source 24 which generates power that is transferred to the electrodes 14 and 18. On a side opposite the electrode layer 14, a lens 26, preferably a concentric Fresnel lens, is formed. Spaced from the lens 26 is a liquid level control plate 28, having an aperture 30 formed therein. Ink, or fluid, 32 is retained between the liquid level control plate 28 and the glass layer 12, and the aperture 30 is aligned with the lens 26 to facilitate emission of a droplet 34 from surface 36. The surface 36 is, of course, exposed by the aperture 30.
The lens 26, the electrode layer 14, the piezoelectric layer 16, and the electrode 18 are formed on the glass layer 12 through known photolithographic techniques. The liquid level control plate 28 is subsequently positioned to be spaced from the glass layer 12 to establish a focal gap. The ink 32 is fed into the space between the plate 28 and the glass layer 12, e.g. the focal gap space, from an ink supply (not shown).
Acoustic ink printheads of the type incorporating emitting elements as described above typically have components that are bonded together with epoxy material. Epoxy bonded heads have the disadvantages of 1) experiencing epoxy delamination by the ink and 2) requiring increased manufacturing time resulting from the excessive cure time inherent in use of epoxy materials. Moreover, many types of epoxy materials are simply not compatible with the types of ink used in acoustic ink printing. Another disadvantage of the heretofore known types of acoustic emission heads is that, in such heads, it is difficult to maintain a uniform focal gap, i.e. the gap between the control plate 28 and the glass layer 12 shown in FIG. 1, across the entire emitting surface of the head. Controlling the focal gap is important for purposes of precision in emitting fluid.
It would, therefore, be advantageous to provide a head that is assembled without the use of epoxy. Such a head would be easier to assemble and would avoid the problems associated with the lack of compatibility of certain epoxy materials and the ink. It would also be advantageous to provide a head with improved focal gap control.
The present invention contemplates a new guleless acoustic ink printhead and a method of assembling the printhead that resolves the above-referenced difficulties and others.